Oats forms an integral part of the rotational cropping system on the light sandy soils of the Vaalharts irrigation scheme. This is necessary due to the fact that these soils are usually heavily infested with eelworms which limit the production of other crops (e.g. groundnuts, cotton, maize). Furthermore, a wheat disease called "Take-All" (Gaeumannomyces graminis var. Triciti) can cause large losses of wheat harvests. These problems can be alleviated by the introduction of oats as a rotational crop. As the net income from oats is relatively low, many farmers started to utilize the oats as pastures for beef cattle. Adult cows are mostly used because weaners usually do not reach a satisfactory fat grade in the three to four months of grazing. The aim of this study was to investigate the influence of supplementary energy feeding on the performance of weaners and to compare the performance of adult cows to that of weaners.

MATERIAL & METHODS

Two studies were conducted on irrigated oats pastures at the Vaalharts Experimental Station. In Experiment 1 the effect of supplementary feeding on the growth of beef steers was investigated. Forty Bonsmara type steers (8 months of age) were randomly divided into four groups. Four paddocks of 0.25 ha each were allocated to each of these groups. Each evening animals were kept in kraals where two of the four groups received 500 and 1000 g of maize respectively. The third group was allowed free access to maize while the fourth group was used as a control. During the night, all groups were also allowed free access to oats hay. Groups were rotated weekly between the paddocks allocated to each. Body weight was recorded every two weeks while intake of supplementary feeding was also monitored. Animals were maintained on these pastures for a period of 13 weeks

In Experiment 2, one group of 20 Bonsmara cows and two groups of Bonsmara steers (20 per group) were run on irrigated oats pastures. The cows were rotated between four paddocks of similar size (total area: 3.679 ha) at weekly intervals, while the two groups of steers were also kept on four paddocks each with total areas of 1.797 and 1.811 ha respectively. During the night all groups were allowed free access to oats hay while one group of steers also received a mixture consisting of 20% maize and 20% protein supplement (Voermol SB 100) on an ad libitum basis. Body weight was recorded every two weeks, while intake of hay and supplementary feeding was also monitored. Animals were maintained on these pastures for a period of 16 weeks.

During the later stages of both experiments, additional animals of similar age were added to the different groups to utilize surplus oats pastures for the calculation of total number of available grazing days for each group. Average daily gain was calculated for each animal by regression of body weight on experimental days. Statistical analysis were performed using the GLM procedures of SAS (Littell et aI., 1991).

RESULTS & DISCUSSION

The results of Experiment 1 are summarised in Table 1.

From Table 1 it is evident that supplementation had no effect (P = 0.61) on average daily gain, probably as a result of reduced pasture and hay intakes. Similar results have been reported when starch supplementation has been supplied (King et al., 1997; Pienaar et al., 1990). This resulted in more grazing days available in the supplemented groups. The net result was that the supplementation of 500 g of grain resulted in a 12.5% higher margin compared to the control.

The results of Experiment 2 are summarised in Table 2. Again, no significant difference (P = 0.69) were obtained in average daily gain between the different groups. Beef production per hectare, however, was twice as high in the steer groups than in the cow group due to the fact that twice as many steers could be kept per hectare compared to the heavier cows. Supplementation of steers also had no effect on growth rate, which is in accordance with the results obtained in Experiment 1. The effect of starch supplementation on voluntary feed intake of oats pastures was again reflected by five more grazing days available in the supplemented group. The margin for unsupplemented steers was 171 % higher than for cows and 12 % higher than for supplemented steers.

CONCLUSION

The results of this studies confirms that large quantities of starch supplementation has little effect on growth rate, possibly as a result of decreased voluntary intake of the pasture. It can also be concluded that oats pastures should rather be utilised by young growing animals than adult cows.